Tree hollows constitute crucial habitats for fauna and can bufer ambient environmental conditions. he latter property should be especially relevant during extreme weather conditions, which are forecast to increase under anthropogenic climate change. We investigated the bufering capacity of Eucalyptus oleosa F.Muell. ex Miq. subsp. oleosa tree hollows in semi-arid southern Australia for 28 days under a wide range of ambient temperatures. Tree hollows provided more stable microclimates than ambient conditions, maintaining lower temperatures and higher humidity during the day and higher temperatures and lower humidity during the night. Daytime bufering capacity increased slightly with depth and we recorded a maximum bufering of 15.1°C below ambient temperatures. Maximum day time bufering capacity increased at a rate of approximately 0.6°C per 1°C increase in ambient temperature, meaning that maximum bufering capacity was reached during the hottest periods. he high bufering capacity of tree hollows suggests that old trees with deep hollows are important in facilitating the persistence of fauna during extreme weather events. herefore, protecting old-growth forests and vegetation remnants that are rich in tree hollows is an important strategy for mitigating the impact of climate change on fauna.

Carmichael et al. (1) used stable isotope analysis to define the food webs of horseshoe crabs, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, and also found that these animals forage within relatively small areas of estuaries. In this study, we used field measurements and stable isotope analysis (2) to determine whether the trophic position and site loyalty described by Carmichael et al. (1) in Pleasant Bay were also found in two additional Cape estuaries, Stage Harbor and Barnstable Harbor, and to determine how the trophic position of horseshoe crabs might change as adult crabs grow. Increased population densities and the resulting anthropogenic wastes within watersheds increase nitrogen loads to estuaries (2). Pleasant Bay is part of the Cape Cod National Seashore Reserve and has a low nitrogen load due to the lack of developed land in its watershed (1). Stage Harbor and Barnstable Harbor have relatively greater population densities in their watersheds, and as reported elsewhere in Cape Cod (2), should have greater relative nitrogen loads. The land-derived nitrogen loading rates to the three estuaries are likely to rank in the order of Stage Harbor Ͼ Barnstable Harbor Ͼ Pleasant Bay (3, 4). Since increased urban development results in heavier nitrogen signatures of estuarine water and biota (2), we opted to study these estuaries with different land use in their watersheds to take advantage of potential resulting differences in ␦ 15 N and ␦ 13 C signatures (5, 6). We collected samples during July 2003 at a site in Barnstable Harbor and three sites in Stage Harbor in Cape Cod. We measured the size of horseshoe crabs as the width at the widest region of the prosoma (7). To obtain samples for isotope analysis, we sampled tissue from the last two segments of the second or third walking leg of adult horseshoe crabs (1). To identify some potential foods of horseshoe crabs, we also sampled quahogs (Mercenaria mercenaria), polychaetes (Nereis sp., Nephtys sp., and Glycera sp.), seston filtered from 1-l water samples, and sediment from two 10-ml sediment cores taken 3 cm deep, which were pooled into a single sample. All samples were dried at 60°C, ground, and sent to the Stable Isotope Facility, University of California, Davis, for mass spectrometry. The ␦ 13 C signatures of the horseshoe crabs suggest that their diet may have included a mix of polychaetes and quahogs (Fig. 1a). Quahogs, in turn, assimilated carbon from a mixture of seston and sediment, judging from their position relative to values on the ␦ 13 C axis. The carbon in seston and sediment was likely initially derived from phytoplankton and macroalgal organic particulates (gray lines in Fig. 1a) (8). Polychaetes seemed to belong to a separate branch of the food web, since they had relatively heavier signatures, and most likely incorporated a mix of carbon from